1. Field of the Invention
This invention relates to novel acetal copolymers and methods for their preparation. More particularly, this invention relates to novel high molecular weight elastomeric copolymers of 1,3-dioxolane and 1,3-dioxepane. These copolymers are noncrystalline, not only at room temperature (about 25.degree. C.) but at temperatures as low as -120.degree. C. and below. They also have low glass transition temperatures (Tg). Hence, they are useful as low temperature elastomers, and can also be used as adhesives for bonding glass and metals. In addition, they can be blended with conventionally prepared crystalline oxymethylene homo-, co- and terpolymers to improve the impact properties of articles made therefrom.
2. Description of the Prior Art
Commonly-assigned U.S. Pat. No. 4,788,258, issued Nov. 29, 1988 to Collins, et al., discloses and claims low Tg trioxane/1,3-dioxolane copolymers which are non-crystalline at room temperature and above (although they can be made to crystallize at temperatures below room temperature). Those copolymers have a dioxolane content greater than 65 mol percent and less than about 75 mol percent and an IV (intrinsic viscosity) of from about 1.00 to about 2.3, as measured by standard viscometric measurements, e.g., in o-chlorophenol or hexafluoroisopropanol.
Terpolymers of trioxane with 1,3-dioxolane and from about 2 to about 20 weight percent of a formal of a monoethylenically unsaturated aliphatic diol having at least 4 carbon atoms in its main chain--the chain containing the ethylenic unsaturation and bearing the diol's hydroxy groups--such as 4,7-dihydro-1,3-dioxepin (2-butene-1,4-diol formal) and the like, which are non-crystalline at room temperature or above are disclosed in commonly-assigned U.S. Pat. No. 4,758,608, issued July 19, 1988 to Collins, et al. These terpolymers contain greater than 65 weight percent and less than about 75 weight percent dioxolane, and have IV's of from about 0.5 to about 1.5 as measured by standard viscosity measurements.
U.S. Pat. No. 3,480,590, issued Nov. 29, 1969 to May, et al. ("May, et al. I") discloses polymerizing cyclic acetals in the presence of a carbonium or carboxonium hexafluoroantimonate catalyst under substantially anhydrous conditions at a temperature between -100.degree. C. and 150.degree. C. The May, et al. I patent's cyclic acetal monomers include trioxane, tetroxane, 1,3-dioxolane, 1,3,5-trioxepane and 1,3-dioxepane, which are said to be homopolymerizable or copolymerizable with each other or with other polymerizable compounds to give polymers useful for compression, injection, and extrusion molding. Example 7 of the May, et al. I patent relates to the homopolymerization of 1,3-dioxepane in the presence of triphenylmethyl hexafluoroantimonate as a catalyst to give a polymer described as a colorless, slightly tacky, rubber solid.
U.S. Pat. No. 3,422,035, issued Jan. 14, 1969 to May, et al. ("May, et al. II"), discloses polymerizing cyclic acetals in the presence of an iodonium, substituted iodonium, nitryl or nitrosyl hexafluoroantimonate catalyst under substantially anhydrous conditions at a temperature between -100.degree. C. and 150.degree. C. The May, et al. II patent's cyclic acetal monomers again include trioxane, tetroxane, 1,3-dioxolane, 1,3,5trioxepane and -,3-dioxepane, which are also said in this patent to be homopolymerizable or copolymerizable with each other or with other polymerizable compounds to give polymers useful for compression, injection, and extrusion molding. Example 4 of the May, et al. II patent describes copolymerizing dioxolane and trioxane using nitrosyl hexafluoroantimonate as a catalyst to give a polymer having a melting point of 51.degree.-52.degree. C.
U.S. Pat. No. 3,652,465 to Takakura, issued Mar. 28, 1972, discloses polymerizing cyclic acetals such as 1,3-dioxolane, 1,3-dioxepane and 1,3,6-trioxolane using a zinc halide-carbon tetrahalide catalyst system to give homopolymers and copolymers. The patentee describes his products as having the polyether structure and being:
in the form of viscous liquid, grease or solid depending on the types of cyclic acetals and comonomers used and the reaction conditions employed;
sentence bridging columns 3 and 4. Example 8 of the Takakura patent relates to the homopolymerization of 1,3-dioxepane using various combinations of zinc halide and carbon tetrahalide to give products referred to as "grease-like polymers".
U.S. Pat. No. 3,393,157 to Janssen, et al., issued July 16, 1968, describes polymerizing cyclic ethers and acetals using sulfur trioxide (SO.sub.3) as a polymerization catalyst. The reaction is carried out at a temperature of from about -80.degree. C. to 150.degree. C. for a period sufficient to produce a polymer not composed exclusively of oxymethylene groups. Example 10 of the Janssen, et al. patent is directed to the homopolymerization of 1,3-dioxolane to give an 81% yield of a product having a reduced viscosity of 3.2. The polymer of this example is not further characterized. The Janssen, et al. patent indicates that its polymers may vary in form from low viscosity oils to high molecular weight solids, depending upon the monomeric starting materials, the amount of catalyst used, and the other reaction conditions. Such polymers are said by Janssen, et al. to be useful as plasticizers, lubricants, intermediates in the manufacture of plastics, and as plastics having thermoplastic properties.